The Biosensor BIAcore instrument will enable us to directly observe and measure the binding affinities and association/dissociation kinetics of molecular interactions in real time, thus greatly accelerating the process of identifying and characterizing both protein-protein and protein-DNA interactions. The BIAcore instrument contains an immobilized ligand on a sensor chip, and can monitor the adsorption of unlabelled proteins in free solution to the chip by means of surface plasmon resonance detection, that is, changes in the refractive index in the vicinity of the surface of the chip. These changes are directly proportional to the change in adsorbed mass, enabling characterization of biomolecular interactions. The bound material can also be eluted and recovered from the sensor chip, thus allowing identification of previously unknown molecular interactions. This instrument can in fact be used to screen phage display libraries which express scFv sequences, as well as characterize known protein-protein or proteinDNA interactions. The major users of this instrument are all NIH grant recipients and will constitute 80% of the estimated usage. Their projects represent a diverse array of interests that reflect the flexible and highly useful nature of the instrument, and include examination of protein:DNA and protei-protein interaction that regulate transcriptional activation in hypertension, stress, cell cycle, and hormonal signal transduction, as well as mechanisms of vrial envelope binding to cellular surface receptors. The minor users of this instrument represent 20% of the estimated usage, and consist of junior faculty who have not yet received NIH funding; their projects also illustrate the diverse applications to which this instrument can be adapted, including characterization of RNA binding protein interactions with oncogene transcripts, and screening of phage display libraries to obtain cell surface binding peptides and single chain antibodies with unique specificities.